1. Field of the Invention
The present invention relates to a humidifier able to accurately produce a humidified gas stream.
Accurately controlled humidities are required for many applications, particularly in research on the effects of humidity on a wide variety of things and for the calibration of humidity measuring instruments. For some methods of producing accurately known humidities a means of humidifying a gas stream precisely to the point of saturation at a known temperature is required.
In theory, a gas stream in close contact with and flowing across the surface of the liquid with which it is being humidified at constant temperature, approaches asymptotically to the point of saturation (the point of equilibrium where no more vapour can be accepted by the gas). In theory, if the geometry, flow rate and dimensions are suitably chosen the approach to saturation can be made as close as required.
2. Description of the Prior Art
Prior known devices for producing saturated gas include bubble type humidifiers and extended surface humidifiers.
Bubble type humidifiers operate by passing the gas in fine bubble form through the liquid. Such devices whilst being able to produce large quantities of saturated gas suffer two major disabilities. Firstly, as the gas bubbles pass through the liquid gas interface fine liquid particles become entrained in the gas, and secondly as the point of saturation is gas temperature dependent, it is difficult to obtain precision as the gas temperature is not directly controlled.
Extended surface type humidifiers including liquid surface or wick type humidifiers are not well adapted to produce large quantities of saturated gas.
It is an object of the present invention to overcome or at least ameliorate the above-mentioned shortcomings of the prior art.
In the present invention a bubble humidifier and an extended surface humidifier are combined to form an efficient and accurate saturating humidifier A primary bubble humidifier comprises a vessel containing the liquid, usually but not necessarily water, through which the air or other gas to be humidified is bubbled. The gas is then passed to a secondary extended surface humidifier comprising a labyrinth of wicking fully wetted with the liquid. The bubble humidifier is able to produce a gas stream close to the saturation point in a small space with simple equipment but may be inaccurate by having insufficient liquid depth and by producing aerosol spray in the gas stream.
The labyrinth form of extended surface humidifier is very effective at removing spray, and since the gas is already approximately saturated, the labyrinth may be small, as it does not require very high capacity.
A feature of the present invention is the provision of a means for providing a controlled amount of power to balance the latent heat of evaporation of the liquid in the bubble humidifier as a gas stream is humidified.
The amount of energy required is determined by a feedback controller which senses the temperature at a suitable point on or in the humidifier, compares this temperature with the required reference value and thereby derives an error signal which after suitable processing provides a power input to the humidifier to reduce the temperature error to zero or make it negligibly small.
The principle of providing controlled power to balance the power consumed as latent heat of evaporation to maintain the correct gas stream temperature may be extended to the labyrinth humidifier.